Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252007 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 407 PM EDT Tue Oct 25 2016 .SYNOPSIS... Some cold unstable air will bring areas of clouds and unseasonably cool temperatures through Wednesday. A strong storm system impacts the region Thursday into Friday which will bring a period of wintry weather with onset, prior to moderate to heavy rain along with gusty winds with passage. An active, cooler than average weather pattern is advertised over the weekend into next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Through evening... Upper shortwave overhead with cold pool and cold pool moisture generating clouds. The air is dry beneath these clouds, with dew point depressions of 20-25F, so any attempt at showers should dry up on the way down. Daytime heating by the sun is creating a mixed layer up to near 850 mb. Winds in the mixed layer are 20-25 knots, so expect wind gusts in this range. Temps aloft around -5C which will support max temps in the upper 40s and lower 50s. Tonight... ***Freeze Warning expanded a little in RI and SE MA*** High pressure axis remains centered to the west. North-northwest winds continue at night but the winds and diurnal sky cover will diminish with sunset. The northwest flow has been transporting colder air into the region. With this cold air in place, we expect temperatures to fall below freezing away from the coast and the mid 30s to around 40 near the coast. With these values, we expect freezing conditions in the interior including several areas that have not yet experienced a killing freeze. The Freeze Warning continues where previously issued. We have added SE Providence Co. and Eastern Kent Co. in RI where places outside the urban core will be at risk. We have also added Southern Bristol Co. and Southern Plymouth Co. in MA for areas away from the immediate shoreline. Temps aloft around -5C to -6C with ocean temps 14-15C. This 20-degree differential with sustained winds 12 knots or higher will favor bands of ocean effect clouds, possibly a shower. But the direction will favor an offshore fetch that may clip Provincetown and parts of the Outer Cape. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... High pressure builds over the region. This should bring subsidence and mainly clear skies. Winds over the ocean will continue at 10-14 knots sustained, turning more from the north. This may keep some ocean clouds over Cape Cod, especially Hyannis and points east. Sunshine will work on -6C temps aloft to bring max temps in the mid 40s to around 50. Wednesday night... High pressure ridge will be in place surface and aloft through the night. This should provide mainly clear skies and light winds. Depending on specifics of the ridge axis, the north wind over Cape Cod could back around from the northeast, drawing ocean clouds farther west to the Cape Cod Canal. Great Lakes shortwave and associated surface low over the Midwest will approach overnight. Moisture fields show increasing potential for mid and high clouds during the night, but the lower thicker clouds hold off until near sunrise. Based on the light wind prevailing fair skies, we have stayed close to the existing min temp forecast. The coldest temps may actually be reached a couple of hours earlier than normal, with steady or slowly rising temps late at night as the clouds build in. With the dry low level air expected, the lack of any source of lift, and no forecast of measureable pcpn by this system east of the NY border... we will show nil pops through 12z Thursday. && .LONG TERM /THURSDAY THROUGH TUESDAY/... */ Highlights... - Winter weather possible with storm onset Thursday - Moderate to heavy rain with flooding concerns Thursday night - An active weather pattern with near- to below-seasonable temperatures through next week */ Overview... An active weather pattern is in the cards with temperatures near- to below-seasonable throughout the remainder of October getting into November as signaled per consensus of atmospheric teleconnections and accompanying features within the N Hemispheric pattern. In short colder air is being allowed to spill S and wrap into individual systems round the base of a H5 low over the N Canadian maritimes. Subsequently a series of weather disturbances are forecast of which will likely bring a period of snow to areas of the NE CONUS. Further details below. */ Discussion... Thursday into Friday... Potent storm taking aim on the NE CONUS. With onset, an over-running setup of frontogenetical/isentropic lift ahead of a H85 low to which there is the likelihood of wintry precipitation types. Agree with the prior forecaster of the stronger, deeper, colder solution as it would appear a consensus of the forecast guidance agrees upon. That being said and taking in regard near-surface ageostrophic flow, N winds are likely to prevail ahead of the system and keep colder air in place. But the challenge is drier air. How quickly does top-down moistening occur to saturate the column. It would appear that storm onset may be delayed till midday. Then how quickly does warmer air push in, especially at H925. By the time precipitation gets going some areas are likely to be well above freezing. Thinking precipitation moves into the forecast area towards midday starting off as snow W and central, rain elsewhere. Delay W to E by drier air. N winds holding across the interior throughout into the evening hours. Snow accumulation possible over the high terrain, maybe an inch or two on grassy surfaces as supported by the EPS, concluding with influx of warm air quickly at H925, so not expecting much snow accumulation. Concern as to interior valleys and whether a wintry mix occurs with shallow cold air. But given onset delay in precipitation, valleys are likely to warm around freezing with diurnal heating. Thinking a marginal event given the time of the year, synoptic setup, timing of system. Not thinking the need for winter weather headlines. As the storm sweeps the area, will transition to a strongly dynamic, QG-forced event. Strong forcing of deep layer moisture with omega values up to 50 microbars per second, moderate to heavy rain is more than likely with isolated issues of urban to poor drainage flooding given the progressive nature of the storm. Thunder likely along with gusty S winds of 30 to 40 mph mostly over S/SE coastal New England, as supported by CIPS analogs. As the storm exits, strengthening and invoking dynamical cooling, can not rule out a return of snow for the high terrain in regions of trowaling moisture behind the system, but drier air moving in may rob moisture in better snow growth regions making any outcomes brief with little accumulation for N/W MA. Will continue mention of hazards with respect to moderate to heavy rain and leaf-clogged drains in the hazardous weather outlook. This along with gusty S winds which could result in isolated to scattered wind damage for a brief period of time. Bulk of impacts Thursday night. Friday... Storm lifts out behind which moisture trowals and colder air works in. May see snow linger across the high terrain per cyclonic flow and favorable environment to invoke lift upon residual moisture. Blustery NW flow, scattered to broken low cloud decks, will see both dissipate into the overnight period as a weak ridge of high pressure builds into the region allowing conditions to dry out. Saturday into Sunday... Clipper-like system undergoing decent forcing per low to mid level frontogenesis along a warm front parent to the surface low beneath the left front quadrant of the upper level jet. Signals within the consensus of forecast guidance, but not very good agreement on timing nor on outcomes. An indication of a W to E moderate band of rain where lift and forcing becomes focused. Could potentially turn more seasonable for the area if the system stays N and we get more of a S flow. But at this point a low confidence forecast. Next week... An undulating period of temperatures with an active weather pattern expected. As to details, not a good amount of agreement in the forecast to prevail with. A low confidence forecast. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through evening... VFR. Scattered to broken sky cover from diurnal clouds, but with bases 5000-6000 feet. These should diminish with sunset. Winds in the mixed layer reach 20-25 knots, thus surface winds will gust at times to these speeds. Winds diminish after sunset. Tonight...High confidence. VFR. Diminishing NW winds. Ocean effect clouds may linger on the Outer Cape. Low risk of showers in this area. Wednesday...High confidence. VFR. Winds turn a little from the North but with gusts a little lighter than we had today. Wednesday night...High confidence. VFR. Ocean effect clouds may linger on parts of Cape Cod, especially if surface winds turn N-NE overnight. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Sunday/... Thursday into Friday...Moderate confidence. Cigs lowering to IFR-LIFR into Thursday. Initial breif period of a wintry mix is possible, transitioning to -RA/RA with embedded +RA, TSRA over S/SE coastal terminals along with gusty S winds up to 35 kts through around midnight Friday. Winds back out of the W towards Friday morning, becoming VFR. Saturday and Sunday...Low confidence. Mostly VFR. Perhaps a mix of MVFR-IFR to places N of the Mass Pike Saturday Night into Sunday Morning. W/SW winds throughout. Gusts up to 20 kts. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Through Tonight... NW winds will gradually diminish tonight. Small craft advisories will end piece by piece over the inner waters during the night. Seas will remain up to 5-6 ft on the outer waters, so small crafts will remain in effect there overnight. Wednesday... High pressure builds over the waters. Winds and seas continue to diminish. Seas remain around 5 feet on the outer waters through Wednesday. Continue Small Crafts in those areas. Wednesday night... North winds diminish. Widely scattered ocean effect rain showers east of Cape Cod. Outlook /Thursday through Sunday/...Moderate confidence. Thursday into Friday... Rain beginning late Thursday and continuing through Friday morning, moderate to heavy at times with the expectation of thunderstorms. Majority of impacts overnight. S/SE winds strengthen ahead of a deepening area of low pressure across the region with a brief period of gale force gusts. Seas building 8 to 10 feet, dropping off towards Friday morning and through the day as winds turn out of the W behind a cold front but remain breezy with gusts up to 30 kts. Gale headlines may be needed. Saturday into Sunday... W/SW winds with gusts up to 25 kts, dissipating with time. Will see seas dampen as well. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Freeze Warning from 2 AM to 9 AM EDT Wednesday for CTZ003. MA...Freeze Warning from 2 AM to 9 AM EDT Wednesday for MAZ006-007- 013-014-018-020-021. RI...Freeze Warning from 2 AM to 9 AM EDT Wednesday for RIZ001>004- 006. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ232>234. Small Craft Advisory until 8 PM EDT this evening for ANZ230- 236. Small Craft Advisory until 8 AM EDT Wednesday for ANZ231-251. Small Craft Advisory until midnight EDT tonight for ANZ237. Small Craft Advisory until 7 AM EDT Wednesday for ANZ235-256. Small Craft Advisory until 2 AM EDT Thursday for ANZ250-254- 255. && $$ SYNOPSIS...WTB/Sipprell NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Sipprell AVIATION...WTB/Sipprell MARINE...WTB/Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.